A process using a plasma is widely applied to an etching device as well as a semiconductor manufacturing process and a liquid crystal display device substrate manufacturing process.
The prior art will be described in conjunction with a plasma etching device, shown in FIG. 16, which is taken as an example. In this etching device, a high voltage from a high-frequency power supply 5 is applied between an upper electrode 2 and a lower electrode 3 arranged in a processing chamber 1 and in parallel to each other to generate a plasma 6 from an etching gas by virtue of discharge between both the electrodes so that a semiconductor wafer 4 as an object to be processed is etched by species in the plasma. In performing an etching process, the progressing status of etching is monitored to detect an end point of the etching process as correctly as possible, thereby performing the etching process by only a predetermined pattern configuration and depth.
Techniques including spectral analysis, mass spectrometry and so on have hitherto been used in a method for detecting the end point of etching. Especially, the spectral analysis having a simple device construction and a high sensitivity is widely used, as shown by JP-B-6-28252. More particularly, a specified one of species including radicals or ions such as an etching gas and a decomposition product or reaction product thereof is selected and the emission intensity of an emission spectrum from the selected species is measured. Namely, in FIG. 16, an emission 8 from the plasma is passed through a window 7 so that it is subjected to spectroscopic analysis by a spectroscope 9 such as a monochrometer to extract only an emission component 10 having a predetermined wavelength. This emission component 10 is received by a photoelectric conversion element 11 such as a photomultiplier for conversion into an electric signal and is amplified by an amplifier 12. Thereafter, the amplified component is sent to an end point judging unit 13. In the end point judging unit 13, a temporal change 15 in emission intensity is observed, as shown in FIG. 17, so that the emission intensity at a changing point or the value of first-order differentiation or second-order differentiation thereof is compared with a preset threshold S to determine the end point position E of etching. When the end point is detected, the output of the high-frequency power supply 5 is stopped by a power supply controller 14.
The species to be selected differs depending upon the kind of an etching gas. For example, in the case where a silicon oxide film is etched by use of an etching gas of a fluorocarbon series such as CF.sub.4, an emission spectrum (e.g. 219 nm or 483.5 nm) from its reaction product CO* or an emission spectrum (e.g. 260 nm) from its intermediate product CF* is measured.
With the above-mentioned prior art, the end point of etching can be determined with a simple construction. However, the total area of portions subjected to etching becomes small with the fine delineation of a circuit pattern of a semiconductor device so that the absolute amount of a reaction product is reduced. There results in such a temporal change in emission intensity as shown by one-dotted chain line 16 in FIG. 17. Namely, not only the emission intensity itself is reduced but also the amount of change in emission intensity at the end point position is greatly reduced and a very obtuse waveform is exhibited, which makes the judgement of an end point position difficult. This is a large problem in the prior art.
On the other hand, a high-frequency electric power for plasma excitation is on the order of several-hundred kHz and it is considered that an etching reaction and an emission from a reaction product are synchronous with this frequency. In the prior art, however, the amplifier 12 used for the amplification of an emission signal has a band on the order of about 100 Hz to several kHz so that a DC component is mainly detected by smoothing a periodic emission from a reaction product. Therefore, the prior art has a problem that it does not accurately seize the etching reaction and it is susceptible to the influence of gentle variations in plasma emission or the influence of unnecessary frequency components.
An object of the present invention is to provide a plasma process end point detecting method and apparatus and a semiconductor device manufacturing method and apparatus in which the end point of a plasma process can be detected stably and at a high precision always without being affected by the fine delineation of a pattern to be processed and an external disturbance and to provide a semiconductor device which is manufactured using such a manufacturing method.